The goal of this research is to elucidate the mechanisms that govern cellular differentiation using as a model system the transformation of a growing cell into a dorman spore in the bacterium Bacillus subtilis. Sporulation involves a process of asymmetric division in which the developing cell is divided into large small and large progeny cells that communicate with each other through pathways of intracellular signal transduction. Traditional approaches to investigating sporulation have emphasized mechanisms operating at the level of solitary cells. But recent research additionally reveals antagonistic and cooperative interactions between cells poised to sporulate. Indeed, a major theme of this research is that a cell culture is a mixture in which individual cells are directed toward different fates and express different sets of genes. This proposal addresses important gaps in our knowledge by asking two well-defined questions whose answers are, thus far, only partially known: (I) how do regulatory circuits and morphogenetic events result in the conversion of a cell into a spore? (II) How does sporulation occur in the context of a multicellular community?